Cable networks are communication networks that communicate broadband communication signals between a centralized headend and a plurality of customer premise devices. Cable networks have many forms, but typically include a dispersed network of coaxial cable. Many cable networks further include a substantial portion of fiber optic lines. Such networks are known as hybrid fiber coax or HFC networks. Such networks are common.
Historically, cable networks were employed primarily for the delivery of the television program signals. To this end, the cable network headend transmitted a broadband signal to each subscriber through a hierarchical network of coaxial cable, referred to as the cable plant. The broadband signal was divided into a plurality of channels, each channel occupying an approximately 6 MHz or 8 MHz wide band of the overall broadband signal.
The proper operation of cable systems involves field testing. Because the cable plant is dispersed throughout the entire cable service area, the network can experience damage or other detrimental phenomena in varied, isolated portions of the network. As a result, many customers may have excellent service while a few customers cannot receive one or more channels clearly due to a localized problem. Cable service providers have often used handheld signal measurement equipment to help diagnose problems and perform network analysis.
Historically, the test equipment included an RF signal receiver and circuitry for measuring signals received on select channels of the system. Measurement of a large number of channels provides a rough spectrum analysis of the cable network. Various test devices that measured analog cable television channels were developed.
While the cable television system employed analog NTCS standard television signals for years, cable service providers have more recently been switching over to digital television signal broadcasting because of the better cost/service ratios. Because many of the field test equipment developed for cable networks was specifically designed to test analog cable television channels, new digital cable field measurement technologies had to be developed. Such devices were developed, and typically measured the signal level available on selected (or all) channels of the cable television system.
The latest trend in cable systems is to provide two way high speed data communications through the cable network. A customer may thus use their coaxial cable connection to obtain both audio-visual broadcast programming information and for access to the Internet for electronic mail, downloads and web browsing. The HFC network is further configured to support a specialized form of telephone service known as Voice over Internet Protocol or VoIP.
At present, signal level measurements and other related physical layer measurements still provide useful information in troubleshooting and analyzing network performance. To address the need for more extensive testing of the various services provided to the HFC network customer, new testing equipment and methods have been developed, such as those disclosed in the co-pending patent applications noted above. As set forth in one or more of those applications, a DSAM packetloss or throughput test may be supported using a “ping” message. A “ping” message requires the generation of an Echo Request message in the ICMP protocol and the evaluation of an Echo Reply message. This method of evaluation is effective as long as the Cable Modem Termination Server (CMTS) or other router at the headend responds to Echo Request messages.
Unfortunately, some computer hackers use the Echo Request message to perform a Denial of Service (DOS) attack on a server. A DOS attack includes a bombardment of Echo Request messages on a server. Consequently, many CATV operators who support cable modem operations have programmed the CMTS or other router at the headend to ignore Echo Request messages. Test equipment relying on replies to Echo Request messages for packet loss testing are unable to determine whether the failure to receive a reply arises from the programming of a router or CMTS at the head end or some problem with the cable plant between the test equipment and the CMTS.
Another problem with testing that relies on ICMP messages is the prioritizing that the CMTS or other router at the head end can perform for these messages. That is, the CMTS or router is capable of lowering the priority of ICMP messages. Such action yields inaccurate test results because voice data packets are not transmitted in ICMP packets. Consequently, communication delays arising from ICMP message re-prioritizing do not reflect the communication timing of packets used for VoIP messages and the like.
Therefore, test equipment that does not rely upon ICMP messages for packetloss and throughput measurements is needed.